The frequency band used by mobile phone systems is generally considered to be a plurality of frequency bands. For example, in the case of PDC systems (personal digital cellular telecommunication systems) in Japan, the 800 MHz band (810 MHz to 956 MHz) and the 1.4 GHz band (1429 MHz to 1501 MHz) are used, and in the case of digital cellular systems in the United States, at least the 900 MHz band (824 MHz to 894 MHz) is used for AMPS (advanced mobile phone service) systems, and the 1.8 GHz band (1850 MHz to 1990 MHz) is used for PCS (personal communication service) systems. Furthermore, in Europe, the 900 MHz band (870 MHz to 960 MHz) is used for GSM (global system for mobile communications) systems, and the 1.8 GHz band (1710 MHz to 1880 MHz) is used for DCS (digital cellular system) systems. The reason for such use of a plurality of frequency bands is that the number of frequencies that can be utilized in a single frequency band is insufficient due to an increase in the number of subscribers.
Furthermore, in the case of mobile phones, GPS receivers for GPS systems in which the satellite transmission frequency is set at approximately 1575 MHz have been incorporated into the apparatus. The mounting of an antenna which operates in a plurality of frequency bands is required in mobile phones that thus receive or transmit a plurality of frequency bands. Conventionally, therefore, a planar antenna or small-volume chip antenna has been installed inside the wireless apparatus housing as an antenna that operates in a plurality of frequency bands in addition to the main externally mounted antenna. In such cases, however, the antenna occupies volume inside the wireless apparatus housing, and interferes with the compact construction of the wireless apparatus. Furthermore, when the user grips the mobile phone, the proportion of the internal antenna that is covered by the hand is large, so that there is a deterioration in the antenna characteristics during the use of the mobile phone.
Furthermore, there is also a method in which a single-element helical antenna is used, and this is formed into a multiple resonance antenna by forcibly causing multiple resonance by means of an impedance matching circuit. However, in the case of a retractable antenna using a combination of a single-element whip antenna or helical antenna and a matching circuit, it is difficult to obtain satisfactory antenna electrical characteristics in a plurality of frequency bands. Moreover, it is conceivable that antenna elements that operate independently at respective frequency bands in a plurality of frequency bands might be used as an antenna; in such a case, however, a number of antenna elements equal to the number of frequency bands is required, so that the antenna cannot be made compact, and application is a mobile phone is difficult.
Accordingly, it is an object of the present invention to provide a compact multiple resonance antenna and mobile phone antenna which operate favorably in a plurality of frequency bands.